Timeline of the Past


Earth formed/early atmosphere

4,600,000,000 BCE

The Earth was created after the Sun due to accretion of leftover particles and debris. The formation of the Earth was only the beginning and we still see the Earth changing year by years through erosion and plate tectonics. However in learning more about the formation of the Earth we are able to better understand what makes life possible on our planet.

RNA molecules called ribozymes

4,500,000,000 BCE

A ribozyme is an RNA molecule that is capable of catalyzing specific biochemical reactions, similar to the action of protein enzymes. Some ribozymes may play an important role as therapeutic agents, as enzymes which target defined RNA sequences for cleavage, as biosensors, and for applications in functional genomics and gene discovery.

Atmospheric change

4,100,000,000 BCE - 3,000,000,000 BCE

Early atmosphere formed 4.1 BCE consisted of mainly hydrogen.
Second atmosphere formed 3.4 BCE was due to outgassing from volcanoes, Earth’s second atmosphere consisted mainly of nitrogen and carbon dioxide.
a. First use of H20 as source of hydrogen 3 BCE was significant because water was first used as a source of hydrogen.It takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2.


4,000,000,000 BCE

Protobionts evolve from primitive life. They exhibit some of the properties associated with life, including simple reproduction, metabolism and excitability, as well as the maintenance of an internal chemical environment different from that of their surroundings. It has been suggested that they are a key step in the origin of life on earth.
Lysosomes are organelles that contains digestive enzymes (acid hydrolases). They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents.


3,700,000,000 BCE

Organisms start using photosynthesis to gather energy from the sun. Photosynthesis is the conversion of light energy to chemical energy by living organisms such as plants. It is essential for a number of reasons primarily because one of the raw materials is carbon dioxide which is harmful in high concentration to humans and most other aerobic (oxygen breathing) organisms. One of the "waste" products of photosynthesis is oxygen which is vital for most life-forms on earth including humans.

First sign of ancestral prokaryotes

3,500,000,000 BCE

Prokaryotes are based on what these organisms are not (they are not eukaryotic), rather than what they are (either archaea or bacteria).The differences are that ribosomes in prokaryotes are smaller than in eukaryotes. However, two organelles found in many eukaryotic cells, mitochondria and chloroplasts, contain ribosomes similar in size and makeup to those found in prokaryotes. This is one of many pieces of evidence that mitochondria and chloroplasts are themselves descended from free-living bacteria.

Prokaryotes evolve

2,500,000,000 BCE

Prokaryotes do not have a membrane bound nucleus, mitochondria, or any other membrane-bound organelles. In other words, all their intracellular water-soluble components (proteins, DNA and metabolites) are located together in the same volume enclosed by the cell membrane, rather than in separate cellular compartments. Most prokaryotes are unicellular organisms.


2,500,000,000 BCE

Endosymbiosis explains the origin of mitochondria and chloroplasts. Their origins have been suggested for many structures, including flagella (structures like the tail of a sperm), cilia (hair-like structures that help in locomotion), and even the nucleus — the cell's command center.
Process formed an interconnected tree of life in which organisms have multiple ancestors, even from different domains. As eukaryotes, our ancestors include both the bacteria that became mitochondria, and the archaebacterium that was the host cell.

First eukaryote emergence

2,300,000,000 BCE

Eukaryotic cells may contain several other types of organelles, which may include mitochondria, chloroplasts, the endoplasmic reticulum, the Golgi apparatus, and lysosomes. Each of these organelles performs a specific function critical to the cell's survival. Moreover, nearly all eukaryotic organelles are separated from the rest of the cellular space by a membrane, in much the same way that interior walls separate the rooms in a house. The membranes that surround eukaryotic organelles are based on lipid bilayers that are similar (but not identical) to the cell's outer membrane. Together, the total area of a cell's internal membranes far exceeds that of its plasma membrane.

Emergence of oxygen

2,300,000,000 BCE

Oxygen is one of the most important elements required to sustain life. Without it, our health begins to suffer and/or we die. Unhealthy or weak cells due to improper metabolism lose their natural immunity and are thus susceptible to viruses and lead the way to all kinds of serious health problems. It gives us life but destroys also the harmful bacteria in our bodies without affecting the beneficial bacteria that we need.

First multicellular organisms

2,100,000,000 BCE

Multicellularity has evolved independently at least 46 times,including in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, Magnetoglobus multicellularis or Methanosarcina. However, complex multicellular organisms evolved only in six eukaryotic groups: animals, fungi, brown algae, red algae, green algae, and plants. It evolved repeatedly for plants (Chloroplastida), once or twice for animals, once for brown algae, and perhaps several times for fungi, slime molds, and red algae.

Mitochondria and plastids emerge

1,500,000,000 BCE

Mitochondria and plastids are never made from scratch, but instead arise by the growth and division of an existing mitochondrion or plastid. On average, each organelle must double in mass in each cell generation and then be distributed into each daughter cell. Even nondividing cells must replenish organelles that are degraded as part of the continual process of organelle turnover, or produce additional organelles as the need arises. Most of the proteins in mitochondria and chloroplasts are encoded by special genes devoted to this purpose in nuclear DNA.


650,000,000 BCE - 120,000,000 BCE

a. First known plants - The Devonian Period deposit containing fossils of both zosterophylls and trimerophytes, some of the earliest vascular plants. This indicates that prior to the start of the Devonian, the first major radiations of plants had already happened. The oldest known vascular plants in the Northern Hemisphere are from the Devonian Period.
b. First known animal - During the Devonian, two major animal groups colonized the land. The first tetrapods — land-living vertebrates — appeared during the Devonian, as did the first terrestrial arthropods, including wingless insects and the earliest arachnids. In the oceans, brachiopods flourished. Crinoids and other echinoderms, tabulate and rugose corals, and ammonites were also common. Many new kinds of fish appeared.
c. First backboned animals - Early fish from the fossil record are represented by a group of small, jawless, armoured fish known as ostracoderms. Jawless fish lineages are mostly extinct. An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placoderm fossils. The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. Vertebrates, among them the first fishes, originated about 530 million years ago during the Cambrian explosion, which saw the rise in organism diversity.
d. First land plants - In the Ordovician period, around 450 million years ago, the first land plants appeared. These began to diversify in the late Silurian Period, around 420 million years ago, and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs.
e. Archaebacteria - Archaea are recognized to be a major part of Earth's life and are said to play roles in the carbon cycle as well as the nitrogen cycle. Archaea had been classed with Kingdom Monera and the name Archaebacteria is no longer valid. Archaeas have an separate evolutionary history and are classified with a different domain in the system.

Mass extinctions

540,000,000 AD

Mass extinctions are significant because they teach us what could happen again if we don't learn from history. With foresight, a mass extinction event can be avoided. For example, we could use the history of past climate changes to predict what will happen in the near future, so that we can act to prevent climate change. One of the reasons are that they allow a new system of life (plants and animals) to take foot and flourish with different species better adapted to their environment. For instance, if it hadn't been for the Permian-Triassic extinction (225 Mya) we might still be trilobites crawling on the ocean floor and free-swimming ammonites.